1. Field of the Invention
The present invention relates to a method of detecting orientation of an optical disk drive, and in particular to a method of detecting horizontal or vertical orientations of an optical disk drive prior to a retrieval operation.
2. Description of the Related Art
In recent years, efforts and resources to improve optical disk drives have focused on facilitating data retrieval, wherein the data retrieval depends largely on a motor control system and a servo control system in an optical disk drive.
Conventionally, when an optical disk drive operates to retrieve data from an optical disk, a spindle motor is activated to rotate the optical disk. Then a laser pick up head is moved to an inter track of the optical disk. Next, a laser beam emitted from the laser pick up head is focused on the data layer of the optical disk. Then an object lens is moved for the laser beam following the track on the data layer. Next, a track number is read from a preformatted sector to identify the current position of the laser pick up head. If a difference between the current track and the target track exceeds 312 tracks (500 μm), a long seeking is activated. In long seeking, the laser pick up head is moved by a sled motor for moving the laser pick up head to a position within 50 tracks from the target track. Next, an object lens is moved to follow the laser beam on the track, and a track number is obtained to identify the current position. Next, a short seeking is activated to move the object lens to the target track. Then the data is retrieved.
As discussed above, data retrieval in an optical disk drive is accomplished through many steps. The long seeking process takes a lot of time and affects the data retrieval time. In order to shorten the time of long seeking, the sled motor is controlled by a velocity curve during the long seeking process. In this way, the sled motor can move the laser pick up head to the target track quickly. FIG. 2 is a schematic diagram of the servo control system of a conventional optical disk drive. Using FIG. 2 as an example, optical disk drive 100 retrieves data from optical disk 200 and transfers the retrieved data to an interface 300. The optical disk drive 100 contains a control circuit 110, which controls a spindle motor 120 through a spindle servo 122. The control circuit 110 also controls a focus device of the laser pick up head 130 through a focusing servo 132 and a tracking servo 134. The control circuit 110 also controls a sled motor 140 through a seeking servo 142 to move the laser pick up head 130 on the guide rail 150.
Referring to FIG. 1A, if the optical disk drive 100 is horizontal orientation, the roller of the spindle motor 120 has a direction along a Z-axis, the sled motor 140 drives the laser pick up head 130 on an XY-plane, focus servo 132 moves the focus device along a Z-axis, and the tracking servo 134 moves the focusing device on an XY-plane.
When the optical disk drive 100 is not horizontal orientation, the movement on the YZ-plane of laser pick up head 130 is influenced by gravity. Referring to FIG. 1B, the optical disk drive 100 is vertical orientation. In this case, the laser pick up head 130 on guide rail 150 moves in a direction parallel to the direction of gravitational force. Because of the gravitational force, when the laser pick up head 130 moves upward (+Z direction), it suffers inadequate moving length, and when the laser pick up head 130 moves downward (−direction), it suffers overrunning moving length. The tracking error produced by gravitational force is aggravated in long seeking process.